Method of and means for electrical transmission of pictures and/or characters



TRICAL TRANSMISSION CHARACTERS d Feb. 26, 1941 May 30, 1944- H. LBECK METHOD` OF AND MEANS FOR ELEC OF PICTURES AND/0R File 2 Sheets-Sheet 2 Af-cfv@ s dug,

INVEN-ron l-l. Ll/ ECI( BY 7 ATTGRNEY '.-Patente'd May 30,

UNITED STATES PATENT lOFFICE METHOD F AND MEANS FOR ELECTRICAL TRANSMISSION' OF PICTURES AND/0R CHARACTERS Heinz Lbeck, Berlin, Germany, assignor to General Electric Co., a corporation of New York Application February ze, 1941, serial No. 380,635 v In Germany July 10, 1939 sclaims.` (ci. risac) `is effected, for instance, in a way similar to the action and operation of a conventional typewriter machine, that is, by the keeper of a relay ship with the paper held on a drum or cylinder, with interposition optionally of a ribbon, so that uponthe paper lines of constant intensity, but of different length are produced in accordance with the incoming impulses. These methods are known as printing or typescript methods.

Now, the drawbacks oflsuch electro-mechanical reproduction or reception are essentially ascribable to the difllculty of faithfully recreat ing differences in shading of the original.

l The second class of methods operates in such a way that voltage impulses produced at the sending end and the intensity of which is a function of the brightness of the picture point o r unit, 4are converted at the receiving end into light impulses of a corresponding intensity. These luminous impulses serve to illuminate or expose a coat or` layer (emulsion) responsive to light `actions which when developed results in a reproduction or copy of the original picture or representation,

that is, usually in the form of a negative. This second method offers the fundamental advantage over the method first mentioned that it is possible to transmit dierent shading values, though it inheres the' shortcoming that the incoming picture is not directly viewable or visible, in fact, it must first be developed, and that it is not possible to obtain several copies at the same-time.`

The method of the invention combines the advantages and merits of the said methods, while avoiding the drawbacks thereof. To be more precise, it insures the electro-mechanical recreation of pictures presenting shading values corresponding to the original, and it also allows to make fact that at the sending end electrical potentials I are obtained by ways and means known in the prior art by scanning sequentially thev picture units of the original picture, said potentials corresponding to the vbrightness of the latter. Now, the ensuing voltagesand this is the novel feature of the invention-serve to 'so act upon an -which is caused .to come into pressure relation- `of the potentials.

alternating current that the frequency of the latter is governed and determined by the amplitude fluctuating frequency, if desired, is then transmitted on carrier frequency and is so-fed to the electromechanical recorder means provided at the receiving end that a sequence of points of substantially constant point thickness in accordane/e with the frequency of the alternating current will be recorded. The invention shall now be explained in more detail by reference to the appended drawings.

Fig. 1 isa schematic view in block form of the basic principle of an arrangement adapted to practice the method of the invention.

Fig. 2 is a circuit organization adapted toproduce the alternating current the frequency of which corresponds to the amplitudes of the voltages giving the picture point brilliance.

Fig. 4 is a schematic view of the construction of the electro-mechanical recorder system adapted to the method of this invention.

Figs. 3, 5 and 6 illustrate graphs to aid in the explanation of the operation of applicants system.

` Referring to Fig. 1, I is the sending `drum on which the original picture is fastened. 2 is a source of light the radiations of which by means of suitable .optical means are focused upon the elementary picture or picture point to be scanned at a given instant. Such light asis reected from the illuminated and scanned picture point is conveyed through other optical means to the photo-electric cell 3 in a way well known vin the prior a'rt. What is produced here as a result is a'photo-electric potential the amplitude and value of which is a function of the brilliance of several copies by one and 'the same receiver equipment which are directly visible.

The method of the invention for theelectrical transmission of pictures is predicated upon this the picture point just scanned. Now, according to the invention, the potential produced in the said photo-cell 3 is impressed upon a frequency governing element 4. The latter willcause a more or less great detuning Af of the oscillator i generating a fundamental frequency f in accordance with the value of the photo-electric potential U supplied to it. What thus results in the output circuit of the oscillator is an alternating current having a frequency f-i-Af. In another circuit element I by demodulation as This alternating current ofknown in the `prior art or else by a mixing process, the fundamental frequency f is excluded so that an alternating current having a frequency Af will then flow in the line connected with the output end of 6. The said alternating current is amplified suitably in the device l which Now, to practice the method of this invention,

the seid regmamr Vtute 'r is mluded in the osculation circuit I4 of the oscillator O the fundamental frequency of which is f. According to the size of the grid biasing voltage and thus of the equivalent capacitance of tube T, the os cillator will be varied a more or -less large amount Af. If tube T, for instance, is of a type drum I El a corresponding sequence of points of substantially constant thickness. It will be understood that the transmission is readily feasible in such a way that when scanning a bright picture point the yfrequency of the oscillator 5 will be detuned only to a slight degree, while when a dark spot on the original copy is being scanned, this causes a, marked shift in the frequency of the oscillator. In this manner arrangements may be made so that the frequency of vibration of the recording stylus 9; is high for darkpicture points and small for light ones. paper fastened in the receiver drum l0 is rotated at a constant rate of speed under the recorder stylus 9 vibrating in its longitudinal directions, the result is a, sequence of dots upon the paper which will be so much denser the darker the picture point of the original corresponding thereto. Such a recording or recreation corresponds substantially to the eiiect of reproduced pictures or cuts in newspapers with this exception that in the reproduction of newspaper cuts the'distance betweenvdots is constant, while the density varies, whereas inthe method of this invention, the pointdensityfi's constant, while the inter-point distance varies with the brightness.

Referring to Fig. 2, a detailed description shall now be given by means of an exemplified embodiment in what way the alternating current If, then, the ,s

so that inside a certain range of the grid potential the plate current rises with the grid voltage according to a square law, then, as shall at once bexplained in more detail by reference to Fig. 3, it will be feasible to practice the method in such a way that the frequency shift or detuning lit will be seen that in the case of such a tube where the plate current turnssout to be proportional to the square of the grid voltage, there is produced and transmitted whose frequency varies with the brightness of the picture points. Referring to Fig. 2, Il denotes a unit including a photo-.electric cell 3 mounted at the sending end upon which the light reiiected rom the scanned picture point is projected. The photocell potential U is fed to the direct-current .amplier I2. In the exemplified embodiment here shown an amplifier comprising only one stage is employed, although it will be understood that, if desired, the amplifier could contain a plurality of stages. The amplied photo-potential U is impressed upon theV grid g of reactance tube T` in unit I3. This tube (called a shifter tube) when incorporated in -a circuit organization as shown, behaves like a capacitive reactance, the value of the latter being a function of the slope (mutual conductance) of the tube and thus of its grid potential. By varying the latter by suitable ways and means it is thus feasible to influence the equivalent capacitance of the-'said regulator tube T in-the desired way. 'In the arrangement shown, the anode A is coupled tothe oscillator tube in unit I5 and by a condenser C to the grid g which is connected to the cathode K by a. resistance R. C and'R actas the phase shifter to get the phase quadrature relation of the voltages on the anode and grid to produce the capacitive reactance elect. I

Fundamentally speaking, tube T could also be connected in a, circuit arrangement of a nature so that it will represent an inductive rather than a capacitive reactance; the inductance thereof' is a linear rise of slope S with the grid biasing voltage; in other words, a. straight line as shown inFig. 3. Now, it is known in the art that the frequency detuningor shift Af of the oscillator O is proportional to the equivalent capacity C' of regulator tube T and that the capacity, in turn, is proportional to the slope or mutual conductance of the regulator tube, What can be deduced therefrom is that in the presence of linear form of the slope also the frequency detuning Af of the oscillator will vary in direct proportion with the grid. biasing voltage and thus linearly with the photo-cell voltage U. Now, in the output circuit of the oscillator O there is now available an alternating voltage having a frequency f-l-Af. In one exemplied embodibeing also proportional to the slope of the tube.

ment of thisinvention this alternating current, after having been superposed at the sending end upon a frequency f generated in a second oscillator O' in unit I6 can be demodulated and then put upon a-transxnission channel after having been passed through a low-pass lter TR in unit Il.

In another exemplied'embodiment o the in vention the frequency f+A coming from the oscillator O is fed to the transmission channel, while the beat action and thus the filtering of the frequency Af is effected only at the receiving end. Both these schemes oer this advantage over the methods known in the earlier art that they are far less susceptible to disturbing actions. 'Ihe reason for this is that in the methods of the ealier.art the transmission consists of a sequence of voltage impulses of different amplitudes. These naturally are subject as they travel through the signal channel whether cable or space to attenuation. Since inevitable interfering or atmospheric potential impulses occasionally have an amplitude higher than the signal voltage amplitudes corresponding to the darkest picture elements, there is an ever-present risk and danger, especially in the case of long transmission paths or channels involving serious attennation, of the sIgnal voltage impulses being commore contrasty than the original.

its frequency that is. varied as a function of the p picture element brightness rather than its amplitude. In this Way the'susceptibility to trouble and outside interference is appreciably diminishable.

Referring again to Fig. 2, the alternating current of frequency Af arising at the receiving end is fedto the ampliiier VI in unit lI8 and then to the electro-mechanical recording system I9. The

y electro-mechanical recording system consists, for

' with the result that a sequence of dots is recorded thereon the density of which corresponds to the f frequency Af. The oscillatory system consisting stylus may be supported in a way similar to that used inA loudspeaker systems. In order to insure satisfactory recreation of the picture, the voltage fed to the ,recording system, if desired, may be linearilized in the amplifier V' in such a way that the printing pressure produced by the recorder stylus will be the same regardless'of frequency. In order to stabilize to an adequate degree the printing pressure regardless of the frequency fed to the recorder system, it is recommendable to fix the natural frequency of the recorder system comprising the moving coil and the recording stylus including the fastening or supporting means outside the range of frequencies used for the recording, say', above it. 'I'he recorder stylus itself should preferably be rounded at its striking point in order that injuring of the copying or carbon paper or of the inking ribbon .may be prevented. In order to insure a properly shaded reproduction of the picture a ribbon pref-l erably subjected to continuous travel is provided between the recorder stylus and the paper or the like on which the picture is to be reproduced, similar to a typewriter machine. Moreover, several layers or sheets of paper may be placed upon the receiving drum or cylinder, with sheets of the frequency Af grows more markedly than linear l with the photo-cell voltage Vrather than establishing a straight-line relationship between vthe photo-cell voltage U and the frequency Af, thus resulting in a curve c as shown in Fig. 5. If, on the, contrary, it is desired to secure a softer or less contrasty copy then a dependence as shown by curve d, Fig. 5,-is used. The Adependence illustrated by graphs c and d may be realized, for instance, by using for the regulator tube I3 a type `in which the slope or mutual conductance is a function of the grid biasing voltage as illustrated by the curve, Fig. 6. Working within region B there results essentially a linear relationship between Up While inside ranges C and D the result is a functionas indicated by graphs c andd. In other words, by choosing the grid operating potential suitably it is possible to obtain the desired shape of the slope with the consequence that a compression or an expansion of the shading range in the-recorded recreated picture results.

While in the'foregoing description'of exemplied embodiments of the invention, reference has been made only to a regulator. tube for the purpose of altering the frequency of the oscillator O, Fig. 2 in accordancel with the amplitude of the photo-cell voltages it will be understood that there are other ways and means to the same end. For instance, after adequate amplication the photo-cell currents may be employed for the purpose of varying the biasing magnetization of an iron-,cored moving coil comprised in the carrierfrequency oscillator. y The invention concerns a method of transmitting picturesvel'ectrically. At the transmitter end,

by ways and means well known in the art, electo the brightness of the picture points in the orig-l inal copy. Now, these voltages serve the purpose to act upon an alternating current in such a way carbon paper or the like being interposed between such layers of paper. In this manner, a plurality of copiesl of the incoming `picture may be produced in one and the same working stage and process by the recording stylus.

In order to make the resolution and definition of the incoming picture as satisfactory as possible, the recording stylus, according to another object of this'invention, may be constructed in such a way that it has a width at the pressing or striking point that is smaller in the direction of the line than at right angles thereto. Where this form of construction is used it is possible to make arrangements so that to each picture point 'scanned at the sending end there corresponds a plurality of incoming picture points so that the density thereof becomes so much greater, the darker the shading of the picture point of the original.

In certain circumstances it may be recommendable, for instance, where the original is :dat and devoid of contrast, to make the ensuing copy This end is accomplishable according to a further object of this invention by making arrangements S0 that that the frequency of .the alternating current is governed by the amplitude of the-voltages. This alternating current of varying frequency is fed quency of the alternating current and being substantially of constant intensity is recorded.

Frequency modulation may be insured by means of a shifter (regulator) tube so that by choosing the slope of the latter conveniently it is possible to compress or expand the shading range of the recording at will.

The method here disclosed distinguishes itself from the prior art insofar as it is less susceptible to disturbing actions, and that-several directly visible copies can be made simultaneously.

What is claimed is: i l 1. A system for producing records of subjects, a. scanner for scanning a subject to produce potentials corresponding to subject Vpoint brightingly modulated in frequency, a recorder including a stylus and a coil system for moving the same, the natural frequency of the recorder, including said coil and stylus being outside the frequency range of the wave energy impressed thereon. and connections for impressing said wave energy of lower frequency on said coil sys- 2'..In` a system for producing records of subjects and improving the contrast thereof during the process including frequency controlling reactance, an oscillation generator, a subject scan- A ner for producing potentials which vary in amplitude substantially linearly in accordance with vverm'tlons in the density of the scanned subject,

a variable frequency controlling reactance included in the reactance of said oscillation generator, and connections between said scanner and said variable reactance for controlling said variable reactance by said produced potentials to thereby control the frequency of operation of said generator, the variable reactance being so arranged and constructed that it varies linearly with respect to a selected potential and non-- iinearly with respect to potentials greater and less than said selected potential.

3. In a system for duplicatingl subjects and improving the shading contrast thereof during the duplication process, an oscillation generator having as a frequency determining reactance a reactance tube the mutual conductance of which is a function of its bias, a subject scanner for producing ,potentials which vary substantially linearly in accordance with variations ofthe density of the scanned subject. and connections between the -sc and the reactancetubc for controlling the bias of said reactance tube in accordance with said produced potentials to thereby vary the reactance thereof substantially linearly with respect Vto a selected bias potential and non-linearly with respect to potentials greater and less than said selected potential to thereby modulate the frequency ci the oscillations generated in a corresponding manner.

e. In a system for duplicating plctures, a scanner for scanning a picture and producing potentials corresponding to the picture point density, an oscillation generator including as a frequency determining .controllable reactance, a reactance tube the reactance of which is a function of the tube conductance, said tube having a control electrode the bias of which controls its the contrast of the picture when reproduced is changed.

5. In a system for duplicating subjects. a frequency modulated generator circuit including .a reactance comprising a tube having-an output electrode and a control electrode on lwhich the generated voltages are substantially in phase quadrature to provide in the tube a controllable reactive effect which determines in part the Irequency of the oscillations generated, a scanner for deriving potentials corresponding to the shading of the subject as denoted by point-bypoint scanning thereof, connections between said scanner and tube for applying said potentials to a Vcontrol electrode of said tube to control its reactance, and connections for operating the tube in such a manner that the relation between the reactance provided thereby and the produced potential amplitude is non-linear within the range of variation of the produced potential.

6. A system as recited in claim 4 including,`

connections for transmitting the frequency modulated oscillations, circuits for reducing the Vfrequency of the frequency modulated oscilla- Vwherein oscillations of carrier wave frequency dow. the timing of which oscillations is determined in part by the said included reactance, said reactance including a reactance tube the mutual conductance oivwhich is a function of its bias, a subject scanner for producing potentials conductance, connections between said scanner and said tube for impressing said produced potentials on said control electrode to thereby control the reactance of said tube and consequently control the frequency of the generated oscilla'- tions, the bias of said tube being so adjusted that the vrelation between the generated frequency and the control voltages is non-linear within the a range of the applied control potentials whereby which vary in amplitude substantially linearly in accordance with variations in the density ci the scanned subject. and connections between the scanner and the reactance tube for controlling the bias of said reactance tube in accordance with said produced potentials to thereby vary the reactance thereof substantially linearly with respect to selected bias potentials and non-linearly with respect to potentials greater or less than said selected potentials to thereby modulate the timing of the oscillations owing in said tuned circuit in a corresponding manner. n 1

- LBECK 

